Ultrasonic paper detection

ABSTRACT

Paper jam detection system for use in a printing machine of the type having sheet feed and transporting means including a plurality of ultrasonic detection devices arranged along the paper path of movement to be influenced by each moving sheet, and circuit means for monitoring in timed sequence the effect upon each of the detection devices as sheets are transported.

United States Patent Inventor Edward D. Barton Rochester, N.Y.

Appl. No. 887,952

Filed Dec. 24, 1969 Patented Sept. 7, 1971 Assignee Xerox Corporation Rochester, N.Y.

ULTRASONIC PAPER DETECTION 3 Claims, 3 Drawing Figs.

U.S. Cl 355/3, 355/50, 355/51,355/l6, 271/57 Int. Cl 603g 15/00 Field of Search 271/57;

[56] References Cited UNITED STATES PATENTS 2,973,202 2/1961 Schmeck et al 271/57 3,186,708 6/1965 Hinz 271/57 3,190,641 6/1965 Eissfeldt 271/57 3,232,606 2/1966 Crooks 271/51 3,396,965 8/1968 Dennis et al. 271/57 Primary Examiner-Samuel S. Matthews Assistant Examiner-D. J. Clement Attorneys-.lames .l Ralabate, Norman E. Schrader and Bernard A. Chiama ABSTRACT: Paper jarn detection system for use in a printing machine of the type having sheet feed and transporting means including a plurality of ultrasonic detection devices arranged along the paper path of movement to be influenced by each moving sheet, and circuit means for monitoring in timed sequence the effect upon each of the detection devices as sheets are transported.

PATENTED SEP 7 1971 mg 1 [1F 2 FIG.

INVENTOR. EDWARD D. BARTON [KM Z (g m AT TORNE Y PAIENTEDSEP Han SHEET 2 [IF 2 ULTRASONIC PAPER DETECTION This invention relates to jam detection systems and more particularly to an arrangement of ultrasonic units placed along the path of movement of sheets of paper for insuring the presence of each sheet of paper and their timely movement.

Generally, in machines which require the movement of sheets of paper in timed sequence, such as copiers or duplicating machines, frequent paper jamming occurs due to improper paper feeding, spacing inaccuracies inherent in paper transport systems, counteracting forces produced by processing stations in the machine, and various factors which result in the deceleration or acceleration of paper sheet speeds by the paper-handling system.

in order to overcome jamming, some copiers and/or dupli cation machines employ paper sensing devices which sense the presence of sheets of paper at various points along the path of travel of each sheet. These sensing devices generally take the form of switches actuated by lightweight switch arms arranged in the path of movement of the sheet to be deflected thereby. Other sheet detection systems utilize photoelectric cells combined with light sources for sensing sheet presence or absence, as the case may be. With respect to the sensing devices which utilize switches having mechanical switch arms, the disadvantages are quite apparent, the most important of which is the relatively long lapse of time for each switch actuation to be performed and its effect being transmitted to circuits utilized in 'jam detection systems. For very high speed copiers or duplicators, these lapse times will be completely unacceptable for proper paper jam detection.

Another major disadvantage in this type of sensing device is the fact that the leading edge of each sheet of paper must contact a switch arm which itself may effect the travel of the sheet either as a retarding force, or as a means which skews each sheet out of a predetermined path of travel.

With respect to the use of photocells and light sources, one disadvantage resides in the prospect of the accumulation of dust and other material upon each light source and mating photocell. This accumulation decreases the sensitivity of the sensing device for determining whether or not a sheet of paper exists between a photocell and its light source. Another disadvantage in this system is that the photocell-light source pair will not sense transparent or translucent sheets of paper. The most significant disadvantage of these types of sensing devices will become evident when considering copiers or duplicating machines which utilize photosensitive plates. These types of machines, which are by far the most common in use today, require a light tight enclosure and the use of light sources would necessitate the addition of light baffles or other enclosures in order to insure that the photosensitive surface does not come in light contact with each of the light sources.

The present invention is particularly adapted to avoid these disadvantages enumerated above since there are no light sources required and no mechanical actuation which would impair sheet movement and which are adapted for instantaneous actuation upon the predetermined positioning of a sheet of paper.

. Therefore, the principal object of the present invention is to improve paper jam detection systems for use in paper handling mechanisms.

. It is another object of the invention to utilize ultrasonic detection devices arranged in the path of travel of a sheet of paper.

FIG. 2 is a schematic illustration of an ultrasonic detector device electrically connected .to a circuit for use in the machine, the circuit being adapted to be integrated in a logic system therein; and

FIG. 3 is a schematic illustration of a driver circuit embodied in the jam detection circuit of the invention.

For a general understanding of a typical electrostatic processing copier system in which the invention may be incorporated, reference is had to FIG. 1 in which various components of a typical system are schematically illustrated. As in all electrostatic systems such as a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositelycharged developing material comprising carrier beads and smaller toner particles triboelectrically adhering thereto to form a xerographic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a sheet of paper to which it may be fixed by a fusing device whereby the powder image is caused permanently to adhere to the sheet. V

In the illustrated machine, an original 0 to be copied is placed upon a transparent support platen arranged in an illumination assembly generally indicated by the reference numeral 10. While upon the plate, an illumination system flashes light rays upon the original thereby producing image rays corresponding to the informational areas on the original. The image rays are projected by means of an optical system to an exposure station A for effecting a latent electrostatic image on a moving xerographic plate in the form of a flexible photoconductive belt 12. a

As the belt surface continues its movement, the electrostatic image passes through a developing station B in which there is positioned a developer assembly generally indicated by the reference numeral 14 and where the latent image is developed.

The developed electrostatic image is transported by the belt 12 to a transfer station C through which a sheet of copy paper is moved at a speed in synchronism with the moving belt and whereat the sheet is placed in contact with the image in order to accomplish transfer of the developed image. There is provided a plurality of a sheet feed mechanisms in the form of coacting roller pairs 20, 21, 22, 23 and 24 adapted to transport sheets of paper from a paper handling mechanism generally indicated by the reference numeral 18 to the developed image on the belt at the station C and beyond.

After the sheet is stripped from the belt 12 it is conveyed into a roller fuser apparatus generally indicated by the reference numeral 25 wherein the developed and transferred xerographic powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus at a suitable point for collection externally of the apparatus.

it is believed that the foregoing description is sufficient for the purposes of this application to show a general environment of an electrostatic copier using a jam detection system constructed in accordance with the invention. For further details concerning the specific construction of the electrostatic copier, reference is made to copending application Ser. No. 731,934 filed May 24, 1968 in the name of Hewes et al.

THe paper jam detection system embodying the principles of the present invention includes a plurality of ultrasonic detecting devices each comprising an ultrasonic transmitting transducer or driver adapted to generate ultrasonic waves of a predetermined wave length and an ultrasonic receiving transducer or microphone spaced from the transmitting transducer. The acoustically vibrating elements in each of the transducers may be formed of piezoelectric material which may either convert an alternating electrical signal to mechanical vibrations in the ultrasonic range, or vice versa. Preferably, the piezo elements are in disc form and operate in a mode wherein there is a change in a dimension of the discs in response to the application of voltage betweenthe faces of the discs. These devices are spaced along the path of the sheet paper movement beginning at the paper-handling apparatus 18 and terminating at the exit paper-transporting rollers 24. Along this paper path is an upper plate structure 27 and a lower plate structure 28 spaced therefrom uniformly for the entire path. The plates 27, 28 may comprise a single plate each with all the paper-transporting rollers 20, 21, 22, 23 and 24 extending through slots formed in each plate, or each plate 27, 28 may comprise a series of plates having segments which begin and end adjacent each of the transporting rollers. In any event, sheets of paper being transported are supported on and guided by the lower plate 28.

As shown in FIG. 1, the first ultrasonic detecting-device 30 is spaced immediately adjacent the registration transporting rollers which serve to insure proper registration of each sheet of paper P being separated and fed by the paper-handling apparatus 18. Another ultrasonic detecting device 31 is spaced in pretransfer position immediately before the transfer station C and a third detecting device 32 is positioned in the paper path in a posttransfer position immediately after the transfer station C. Another detecting device 33 is positioned immediately after the fusing device in postfusing position in order to insure that a sheet of paper has emerged from the fusing device in proper timed sequence.

In FIG. 2, the ultrasonic detecting device is shown in detail and connected in a circuit for producing a corrective signal in accordance with the presence or absence of sheet of paper P within the influence of the device. Since each of the detectors 30, 31, 32 and 33 are identical, only one will be described in detail and the construction thereof may be considered as similar to the other device.

The detector device 30 comprises an ultrasonic disc-shaped transmitting transducer 35 mounted in a suitable housing 36 and supported below the surface of the lower conveying plate 28 concentric with a circular opening 37 formed therein. This mounting should be acoustically isolated, and to this end a rubber gasket 38 is shown surrounding the disc 35 in its mounting in the housing 36. The opening 37 is concentric with opening 40 formed in the upper conveying plate 27 and in which an ultrasonic disc-shaped receiving transducer 41 is mounted and acoustically isolated therefrom by means of a rubber gasket 42. In the event the upper plate 27 is not provided in the paper path, the microphone 41 may be mounted by means of a suitable bracket arranged so as to place the microphone in a position immediately above the driver 35. Ultrasonic waves produced by the transducer 35 are transmitted through the openings 37, 40 and are received by the receiving transducer 41 ultrasonically tuned therewith. These waves, illustrated by the letter W, are interrupted when the leading edge of the sheet P projects across the openings 37, 40, which interruption is maintained until the trailing edge of the sheet is moved out of the influence of the device 30. It has been found that a spacing between the transducers 35, 41 of approximately three-eighths of an inch to one-half inch gave optimum results for a particular material in the piezo elements and for resonant frequency thereof. As is known in the use of ultrasonic devices, spacings between transmitting elements and the receiving elements are somewhat critical due to the fact that the acoustic air path between them result in maximum and minimum areas of air density, or standing waves.

In order to obviate the criticality of spacing, the circuits illustrated in FIGS. 2 and 3 are provided. These circuits are devices in order to provide the generation of noise upon the transmitting transducer 35, wherein there is imposed upon this transducer a noise signal comprising random frequencies restricted to the passband of the transducer for causing oscillation by the transducer to change rapidly which, in turn, results in one ofthe frequencies being the correct one for driving this transducer. For a given spacing between the driver or transmitting transducer 35 and the microphone or receiving transducer 41, a certain acoustic frequency could be generated, and that as the space relationship is altered, the

frequencies will change. If operating frequencies for the driver is carried on a repetitive basis and with sufficient speed, the changes in spacing between the driver and microphone would not be a factor.

For a given spacing there is a frequency which will set up a favorable standing wave pattern in the air space between the driver and the microphone which will permit the maximum transfer of energy from one to the other. With the driver being driven with noise frequencies by a driver circuit as illustrated in FIG. 3, the vibrating frequencies induced upon the transducers will vary above and below this resonant frequency and at a fast rate. This sweeping action with the noise band of frequencies will assure that the resonant frequency is attained at some time on a repetitive basis for the transducers. In order to acquire the generation of a noise signal in the driver circuit of FIG. 3, there is utilized a zener diode illustrated by the letter Z in a circuit including a resistor R,, a load resistor R and a capacitor C The resultant noise signal contains all frequencies from a few hertz up to the megahertz region. The driver circuit of FIG. 3 also includes: an amplifier in the form of the transistor T for amplifying the noise signal, a broad band filtering circuit comprising an inductor L, and capacitor C for enhancing the desired band of frequencies as well as attenuating the balance of frequencies, and a second amplifier including the transistor T for effecting the amplification of the resultant desired band of frequencies. The circuitry of FIG. 3 is arranged so that the zener diode current is such that its operating point is very close to the peak of the V,I, characteristic. In the circuit the zener diode produces a noise signal current and stabilizes the collector operating point of the transistor T The load resistor R determines indirectly the zener current, with the noise signal being applied to the collector of the transistor T The transistor T serves as the final amplifier for the modified noise signal which is also applied to one side of an output filter comprising a capacitor C and a variable inductor L The output of the circuit is connected to the driver transducer 35 by way of output terminals 45, 46. A power supply terminal 47 is also provided in order to permit the supply of DC power to the driver circuit. If the applied voltage is high enough, say around +24 volts, all of the drivers for the ultrasonic devices 30, 31, 32 and 33 may be connected to the one circuit illustrated in FIG. 3.

With the circuits illustrated in FIGS. 2 and 3 properly energized by suitable power sources in order to vibrate the transducers 35, 41 at their resonant frequency and with no obstruction in the air space between the transducers 35, 41, the circuit in FIG. 2 will produce a signal indicative of this condition, that is, absence of paper between the transducers. The acoustic waves received by the transducer 41 will generate a small electrical signal which will be transmitted to the amplifier circuit indicated by the reference numeral 50, which will amplify this signal and present the same to the output terminal 51. Upon the presence of a sheet of paper P between transducers 35, 41, the generation of a signal by the transducer 41 will terminate. For utilization of the jam detection system, the terminal 51 is connected to the control logic of the machine indicated by the numeral 52, for controlling operation thereof by means of an electronic timing circuit within the logic. This timing circuit may be of the type which monitors in timed sequence the reception of a signal indicative of the presence of a sheet of paper between a corresponding jam detection device 30, 31, 32 and 33. During normal operation with a sheet of paper being conveyed along its path of movement at the proper speed for machine operation, the sheet must interrupt the acoustical waves between the devices 30-33 in the order in which they are approached by the moving sheet. In corresponding manner, the timing circuit in the logic 52 is arranged so that a signal is generated in the logic when each of the transducer devices is interrupted in proper time. If in the event that a detection device in not interrupted at the precise time in which it is required, another signal will be generated in the logic 52 which will immediately cause the termination of printing operation of the machine. In order to eliminate acoustic interference that may occur because of normal machine electrical noises, the first stage of the amplifier circuit of FIG. 2 has connected in its feedback path, a twin T network 53 which serves to restrict the bandwidth of the amplifier. With this provision, any machine effect on the circuits for the transducers will not be interpreted by the logic for the machine as the absence of a sheet of paper.

From the foregoing it will be appreciated that the use of ultrasonic detecting devices and in the arrangement disclosed with the circuitry therefore that many advantages are evident over other types of monitoring devices. For instance, the presence of printing toners or dust or other foreign materials in the atmosphere surrounding each detection device will have no effect with respect to the detection of paper and that these devices are immune from light source burnout and high ambient light. In addition, the jam detection system arranged in accordance with the present invention is adapted to detect transparent copy as well as opaque copy. it will also be appreciated that there are no interfering structure for impeding travel or which inherently are relatively slow in reaction with respect to the presence of moving paper.

While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth; but is intended to cover such modifications, or changes as may come within the scope of the following claims.

What is claimed is:

1. In a sheet-paper-transporting system having means for conveying sheets of paper along a predetermined transport path in timed sequence, the combination of a plurality of sheet-detecting devices spaced along the transport path at predetermined locations,

each of said devices comprising an ultrasonic generating element adapted to produce ultrasonic waves, and a microphone element spaced from the generating element at a distance to permit the free movement of sheets to be detected therebetween, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present between said elements,

said devices being connected in a circuit having timing means adapted to receive the signal from each of said devices in timed sequence during movement of each sheet being transported by the sheet conveying means, and to effect a corrective signal in the event a signal from one of the devices is not received thereby.

2. A sheet-paper-handling system including transporting means for conveying sheets of paper along a predetermined transport path in timed sequence, said transporting means having a plate structure upon which each sheet is moved durin g conveying thereof,

a plurality of sheet detecting devices spaced along the transport path at predetermined locations,

each of said devices comprising an ultrasonic, generating element adapted to produce ultrasonic waves and mounted on said plate structure, each of said devices also including a microphone element spaced from the generating element at a distance to permit the free movement of sheets therebetwe'en, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present in saidplate structure and between said elements,

said devices being connected in a circuit adapted to receive the signal from each of said devices in times sequence during movement of each sheet being conveyed on said plate structure and to effect a corrective signal in the event a signal from one of the devices is not received thereby.

3. In a printing machine having a photosensitive printing member, means for feeding and transporting sheets of paper along a predetermined path and an operating circuit for effecting the on-off printing operation of the machine, the combination of a plurality of sheet-detecting devices spaced along the path at predetermined locations,

each of said devices comprising an ultrasonic generating element adapted to produce ultrasonic waves and a microphone element spaced from the generating element at a distance to pennit the free movement of sheets to be detected therebetween, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present between said elements,

said devices being connected in a circuit having timing means adapted to receive the signal from each of said devices in timed sequence during movement of each sheet being transported by the sheet feed and transporting means, and to effect a corrective signal to the operating circuit of the machine for terminating the printing operation thereof in the event a signal from one of the devices is not received thereby. 

1. In a sheet-paper-transporting system having means for conveying sheets of paper along a predetermined transport path in timed sequence, the combination of a plurality of sheet-detecting devices spaced along the transport path at predetermined locations, eacH of said devices comprising an ultrasonic generating element adapted to produce ultrasonic waves, and a microphone element spaced from the generating element at a distance to permit the free movement of sheets to be detected therebetween, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present between said elements, said devices being connected in a circuit having timing means adapted to receive the signal from each of said devices in timed sequence during movement of each sheet being transported by the sheet conveying means, and to effect a corrective signal in the event a signal from one of the devices is not received thereby.
 2. A sheet-paper-handling system including transporting means for conveying sheets of paper along a predetermined transport path in timed sequence, said transporting means having a plate structure upon which each sheet is moved during conveying thereof, a plurality of sheet detecting devices spaced along the transport path at predetermined locations, each of said devices comprising an ultrasonic generating element adapted to produce ultrasonic waves and mounted on said plate structure, each of said devices also including a microphone element spaced from the generating element at a distance to permit the free movement of sheets therebetween, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present in said plate structure and between said elements, said devices being connected in a circuit adapted to receive the signal from each of said devices in times sequence during movement of each sheet being conveyed on said plate structure and to effect a corrective signal in the event a signal from one of the devices is not received thereby.
 3. In a printing machine having a photosensitive printing member, means for feeding and transporting sheets of paper along a predetermined path and an operating circuit for effecting the on-off printing operation of the machine, the combination of a plurality of sheet-detecting devices spaced along the path at predetermined locations, each of said devices comprising an ultrasonic generating element adapted to produce ultrasonic waves and a microphone element spaced from the generating element at a distance to permit the free movement of sheets to be detected therebetween, said microphone element being arranged to be influenced by the ultrasonic waves generated from said generating element and adapted to effect a signal when a sheet is present between said elements, said devices being connected in a circuit having timing means adapted to receive the signal from each of said devices in timed sequence during movement of each sheet being transported by the sheet feed and transporting means, and to effect a corrective signal to the operating circuit of the machine for terminating the printing operation thereof in the event a signal from one of the devices is not received thereby. 